1. Field of the Invention
This invention is generally in the field of a power-off hold element for operating in cooperation with an actuator and a process for operating a power-off hold element for operating in cooperation with an actuator.
2. Description of Prior Art
U.S. Pat. No. 5,630,671 to Larson, “Locking Device for a Bearing Assembly,” which is incorporated herein by reference, discloses a locking device for a bearing assembly, which uses an annular ring that expands and contracts to accept and hold a ball end.
U.S. Pat. No. 4,637,944 to Walker, “Process and Device for Temporarily Holding and Releasing Objects,” which is incorporated herein by reference, discloses a process and device for temporarily holding and releasing objects, using the SMP modulus change to hold material.
U.S. Patent Application Publication No. 2003/0127784A1 to Tom S. Davis “Spacecraft Isolator Launch Restraint” which is incorporated herein by reference discloses a spacecraft isolator including shape memory alloy components that are electronically heated to unlock the isolator. The isolator can be manually unlocked with an adjustment bolt.
U.S. Patent Application 2003/0173715A1 to James T. Grutta et al. “Resistive-heated composite structural members and methods and apparatus for making the same” which is incorporated herein by reference discloses a composite structural member, method, and apparatus for making the same. The composite members are formed by resistive heating of the composite material using an electric current with sufficient voltage through the composite. The resistance of the composite material creates an energy loss in the form of heat, melting the matrix of the composite material and allowing the composite material to be shaped in any desired manner.
U.S. Pat. No. 6,388,043 to Langer et al. “Shape Memory Polymers”, which is incorporated herein by reference, discloses shape memory polymer compositions, articles of manufacture thereof, and methods of preparation and use thereof. The shape memory polymer compositions can hold more than one shape in memory.
Only a few shape memory polymer systems have been described in the literature (Kim, et al., “Polyurethanes having shape memory effect,” Polymer 37(26):5781-93 (1996); Li et al., “Crystallinity and morphology of segmented polyurethanes with different soft-segment length,” J. Applied Polymer 62:631-38 (1996); Takahashi et al., “Structure and properties of shape-memory polyurethane block copolymers,” J. Applied Polymer Science 60:1061-69 (1996); Tobushi H., et al., “Thermomechanical properties of shape memory polymers of polyurethane series and their applications,” J. Physique IV (Colloque C1) 6:377-84 (1996)). These documents are incorporated herein by reference.
Examples of polymers used to prepare hard and soft segments of SMPs include various polyethers, polyacrylates, polyamides, polysiloxanes, polyurethanes, polyether amides, polyurethane/ureas, polyether esters, and urethane/butadiene copolymers. See, for example, U.S. Pat. No. 5,506,300 to Ward et al.; U.S. Pat. No. 5,145,935 to Hayashi; U.S. Pat. No. 5,665,822 to Bitler et al.; and Gorden, “Applications of Shape Memory Polyurethanes,”
U.S. Pat. No. 6,494,433 to Mastrangelo et al. “Thermally activated polymer device” which is incorporated herein by reference discloses microfluidic device adapted for use with a power source.
U.S. Pat. No. 6,522,953 to Schneider “Thermal polymer clamping tool” which is incorporated herein by reference discloses a thermal polymer clamping tool. An electrochemical actuator after initial setup is actuated to melt a polymer, forcing a piston assembly and a bearing to shift the threaded shaft longitudinally against a spring, moving the clamping elements apart a short distance to release or receive a work piece. The electrochemical actuator is then deactivated, allowing the spring to expand, clamping the work piece between the clamping elements with the selected force.
Shape memory is the ability of a material to remember its original shape, either after mechanical deformation, which is a one-way effect, or by cooling and heating, which is a two-way effect. This phenomenon is based on a structural phase transformation.
The first materials known to have these properties were shape memory metal alloys (SMAs), including TiNi (Nitinol), CuZnAl, and FeNiAl alloys. The structure phase transformation of these materials is known as a martensitic transformation.
Proceedings of the First International Conference on Shape Memory and Superelastic Technologies, SMST International Committee, pp. 115-19 (1994) which is incorporated herein by reference. The SMPs that have been developed thus far appear to be limited to being able to hold only one temporary shape in memory. It would be advantageous to provide SMPs that are able to form objects, which are able to hold more than one shape in memory.
Also known in the prior art is a phase change actuator such as a paraffin actuator. This actuator utilizes the elimination of shear strength upon melting and/or thermal expansion of paraffin. This actuator has implicit power-off hold because the paraffin can be solidified in place to hold a given displacement. This actuator has the disadvantage of its speed. The speed relies on heating and cooling of the actuator element itself. What is needed is a material for power-off hold element for operating in cooperation with an actuator.